Magnetic analysis



NOV. 16, 1937. v ZUSCHLAG 2,098,991

MAGNETIC ANALYSIS Filed April '23, 19556 INVENTOR Theodor Zuo'cfi lay ATTORNEYS some Nov 16,1937 I PATENT OFFICE Theodor 2mm". West Ens'icwood, n. 1., as-

- .sitnor, to Magnetic Analysis a corporatiofi of New York a plication April as, use, Serial No, 15,945 scam. '(Cl. ms-.188)

This invention -is concerned with the determlnation o! the-metallurgicalcharacteristics such as hardness, toughness, chemical analyses, etc.,

of magnetizable bodies and contemplates animjg' proved apparatuswhereby this iniormation is ob ained by magnetic means.

a magnetizable body is introduced into inductive relationship with a secondaryfcoil in which there is an induced alternating potential 30 it will aiiect both thephaseand amplitude of this potential- Ii" this firstpotential is then opposed by a second potential of the same phase and amplitude, neutralization wlll'occur and there will be no measurable resultant potential. Ii then 3 the first magnetizable bodyis-replaced by a second magnetizable body of diiferent metallurgical characteristics a third potential difiering from the first and second potential in either or both phase and amplitude may result. If the third and second potential are now opposed in a circuit either a phase conflict or a difi'erential potential, or both, may arise. The presence of either a phase conflict or a dlfierential potential than indicates that the second magnetizable body is magnetically or electrically diflerent from the first magnetizable body.

Certain characteristics of magnetlzable bodies are manifested chiefly by potential difierence, and other characteristics bring about changes in the phase of an induced potential with a resultant difierentiai current-l Thus, difierences in cross-section. of mag'netizable bodies ordinarily give rise" to variations in the amplitude of airinduced potential, whereas differences in hardness usually-alve :rise to phase conflicts. When a comprehensive analysis is desired, it is necessary, therefore, to investigate changes in both amplitude and phase.-. r

The instant apparatus facilitates the making of such an investigation.

Considered briefly, the apparatus comprises a primary exciter coil disposable in inductive relationship with a magnetizable body to be investigated-means for energizing the exciter'coil with 4 an alternating current, a secondary coil disposed in inductive relationship withthe exciter coil,

' and a circuit connected to the secondary coil wherein auxiliary potentials may be introduced to neutralize a potential resulting frozn'the secondary coil andwhereln the phase of this poten- .tial may be varied. This circuitalso contains -.mixina transformers which with appurtenant apparatus permit the observation of changes in amplitude or phase of the secondary coil potential 55 due to a change in the metallurgical character'- the potential to be investlmted.

istics of a m 1 etizable body inductively associated with the ndary coil.

Considered in somewhat greater detail this cirr cuit associated with the secondary coil contains V p a phase shifter whereby the phase of the induced potential of this cell. may be varied at .will, and also contains adjustable resistance means (for example, potentiometers) whereby two 90 phase displaced components may be introduced to neutraliae the induced potentialoriginating in the secondary coil whatever its phase may be.

In practice, a standard magnetlzable body of known character is first placed ininductive relationship with the secondary coil and the exciter coil. .By adjustment of the phase of the resultant induced potential, and by compensating the phase-adjusted potential by the introductionof the two 90 phase displaced auxiliary potentials a neutral condition is obtained, and there is no indication of potential in the circuit. If, thereafter, the standard magnetizable body is replaced by a magnetizalole body which is metallurgically dissimilar, indicating devices in the circuit will immediately show the presence of a phase confiict or a change in the amplitude of the induced potential.

The apptus will be more thoroughly understood in the light ofthe following detailed description, taken in conjunction with the accompanying single figure which is a wiring diagram oi a presently preferred'iorm of the apparatus of my invention.

Referring now to theflgure it will be seen that 'an exciter coil t is connected in series with an nated. In operation there is a potential of about volts across the generator and the current in the exciter coil varies from 8 to 10 amperes depending upon the size of. the material undergoing examination. The output of the generator should be single phase. Current of any commercial frequency may beu'sed.

Disposed adjacent the exciter coil,'and preferably concentrically within the-exciter coil is a "specimen secondary coil H.111 which is induced The artificial standard amat Alternating potentials set up in this coil I! are, in effect, opposed in the circuit to a resultant alternating potential corresponding in phase and amplitude to the potential which should be set up in the coil i2 if the metallurgical characteristics of a specimen disclosed in the test coil assembly were those desired. When the two opposed potentials are equal in phase and amplitude, there is no resultant potential and no indication is given by the apparatus. If, however, the specimen in the test coil assembly does not have the desired magnetic or electrical characteristics,v a difierential potential will be set up, or there will be'a phase shift between the two opposed potentials. In either case the apparatus will indicate the changed condition, and advise the operator to reject the specimen.

The specifnen" coil i2 is connected to a phase shifter 55. ,The phase shifter comprises a foursided bridge. In two opposed sides of the bridge, are disposed fixed condensers 56, 51. In the other two opposed sides of the bridge are disposed two adjustable resistors 58, 59, which may be adjusted simultaneously. The two corners of the phase shift bridge intermediate the connections to the specimen coil 2 are connected to'the inputside of an amplifier 54, the output leads of. which are connected to a high impedance primary coil 69 of a matching transformer 6|.

The amplifier is placed in the circuit to off set the voltage reduction in the matching transformer which would otherwise decrease the indications of metallurgical differences to an ex-,

cessive degree. Any suitable type of voltage amplifier may be employed.

' The apparatus contains four mixer transformers, numbered respectively, 69, 10, 'II and 12. Each transformer is provided with two primary coils, numbered respectively, 65 and I8, 66 and ll, 80 and 61, and 8| and 68. The function-of these mixer transformers will be made clear" hereinafter.

Continuing with the description of the circuit, the secondary coil 62 of the matching transformer is connected in series with a switch 63, and the primary coils 65, 66, 61 and 68, respectively, of the mixer transformers 69, 19, H, 12 This series circuit is completed by a connection from primary coil 68 through the sliders and centertap of a potentiometer l3, and the center-tap and slider of another. potentiometer 62A.

Potential for the primary coils I8 and II of the mixing'transformers 69 and I0, respectively, is supplied directly from the primary alternating current source 26 through a circuit which comprises a. current limiting resistor M, a primary coil I5 of a 90 phase shifting transformer .16, the potentiometer 62A through its ends, the coils I1 and 18 of the mixing transformers I8 and '68, and the alternating current source 26.

Potential for the primarycoils 88 and H of the mixing transformers H and 12, respectively,

' is-supplied from a secondary coil 18 of the phase degrees between the currents in primary coill 16- source 26.

ical coil l2 through the two matching transformers and the phase shift bridge. Two other potentials, 90 out of phase with each other may also enter this circuit through the potentiom eters 62A and 13.

The primary coil s ll and i8 of the mixing transformers l0 and 69, respectively, receive primary current from the alternating current source 26, and are connected in series opposition with each other. The primary coils 68 and 8| of the mixing transformers H, 12, respectively, receive electrical impulses 90 phase displaced from the primary potential through the second-- ary coil of the 90 phase shifting transformer and are connected to each other in series opposition. e e v Each of the mixing transformers 69, 18, ii, 12 is provided with a center-tap secondary coil numbered respectively 83, 84, and 86. These secondary coils are connected to rectifier tubes- 81, 88, 89 and 90, respectively, although the mode of connection is different. Thusjthe mixing transformers 69 and i2 areeon'nectedto the plates of rectifier tubes 81 an? 90, while ends of the secondary coils 84 and 5 of. the mixing transformers 10, II are connected to the cathodes of rectifier tubes 88 and 89.

The two cathodes of the rectifier tube 81 are connected to. the two plates of the rectifiertube 88 through the ends, of a balancing potentiometer 9|. The two plates of the rectifier tube 89 are connected to the two cathodes of the rectifier tube 90 through the ends of another balancing potentiometer 92. The slider of the balancing potentiometer 9| is connected to the slider f of still another potentiometer 98, and the slider of the potentiometer 92 is connected to the slid of. zero center direct current galvanometers 95 and 96. The circuit containing the two potentiometers, the two sensitivity control potentiome-' The two sensitivity control poters, the two zero center direct current galvan-- ometers, the four rectifier tubes and the four sensitivity controlpotentiometer with the center point cream of the secondary coils 83, 84, 85, 86 of the mixing transformers.

The mode of operation of this artificial stand! ard circuit and the functions of its various pieces of equipment will now be described.

It is first necessary to consider the action of the four mixing transformers. Taking, for example, the pair of mixing transformers 69am! 18, it will be seen that the primary coil 65 of the transformer 69 receives a current (designated hereinafter as X) from the secondary coil of the second matching transformer 6|. This current is derived from electrical impulses set up in the specimen coil |2 through the matching transformer, the amplifier and the phase shifter bridge. The other primary coil, I8 of the mixing transformer, receives a current (hereinafter designated s Y) directly from the alternatingcurrent ..'1he, currents' x andfi'Y'are necessarilyof the I i same'frequency, but maybe displaced from each other by a phase angle 0. The two primary coils l8 and '65 are as shown arranged so that their is direction of winding is the same; in other words,

they create an electromagnetic flux'by addition. I The secondary potential produced. in the secondary coil 83 of this matching transformer is, therefore, proportional to the vector summation of 7 10 the potentials in the primary coils 66 and 18.;

V Now consideringthe matching transformer, numbered i0, it will be seen that the same currents X and Y are also supplied to it, but inasmuch-as its two primary coils- 85 and I1 are l5 op'positely,.they create a resultant electromagnetic flux proportional to their difference and the secondary coil 84 of the matching transformer I .will have a potential proportional to the vector difference 'of (the potentials in coils 86 and 11.

V20 The secondary potentials of the mixing transformers 69 and iii are both rectified and opposed to each other throughithe potentiometer 8i. The

galvanometer 95 thus produces a reading which is e function of the two primary potentials intro- 25 duced into the two mixingtransformers and also of the angular phase displacement 0 between these twopotentials. Amore elaborate discussion of the functions .of the mixing transformers is contained in my copending application Serial :No; 33,855, filed July so, 1935.

The two mixing transformers Ii and 12 with their appurtenant apparatus function in the same manner as the mixing transformers and as Just-described, except that a currentYi, which, 35 is 90 outoi phase withthe current Y, is'substituted. The result isthat the reading of the .galyanometer 98 is a function of-the potential of current X, the potential of current-Y1 .and an angle" 01 representing the phase displacement between. the two potentials.

1 The net result of the action of the four mixing transformers and the circuits connectedto' 'their secondarles is to indicate differences of i tfwdright angled components of the potential of current x from two other right angled-compofnent's represented by the potentials of currents j" Yand Y1. A metallurgical difference related to either am'agnetic or an electrical variation may the potential of the current x. t By means of the phase shifter bridge is the f phase :of the current x'derived from the secondary coil of the second matching transformer may specimen'placed in inductive relationship with the specimen coil It, the two galvanometers SI and, both may be made to read zero. Thereafter, if this standard magnetizable specimen is 7 replacednby one having different magnetic or j electrical'characteristics, these different characv teristicslviil, be indicated at either galvanometer and warn the operator thatthe'material is not similar to the predetermined standard and should l replacedbythegoodbar; ll

is bereiected. H 1

1 be manifested in either or both components of.

o l the apparatus The adjustment of the metallurgical analysis circuit is made as follows:

With the switch 63 opened so that nov potential is supplied 'to the coils u, u, n, so, of the respec- 5 tive mixingtransformers, and with current being supplied to the coils 11, 18 of two mixer transformers directly from the alternating current source and to the primary coils I. and If oi the other mixer transformers from the secondary m r coil of the phase'transformer, the galvanometers 95, 96 are made to read zero by adjusting the sliders of thepotentiometers SI and 92.

Next, with a standard specimen of known and desired character inserted substantially symmetrically in the test coil assembly, the switch 83 is closed so that all of the primary coils of the 'mixer transformers are energized;. An electromotlve force now has been set up in the. specimen coil 20 i2 and transferred through the matching transformers and the phase shifter bridge (which is set at an. arbitrary'point) to the secondary coilof the matching transformer 8|. The electromotive force thus induced in the secondary or output coilof the matching transformer is'then v compensated byadiusting the position of the sliders on the potentiometers 62A and 13 until the two galva'nometers again attain zero positions.- 'Bearing in mind thatthe"curren ts flowing through thepotentiometers 82A and it are 90, phase displaced from each other it" will h clear that the 'electromotiveforce in the secondary of the'second'matching transformer has now been compensated with regard to these two com:

ponents.

The artificial standard circuit is now ready "to operate. Iffthe standard specimen is now replaced by a second and metallurgically-disslmilar i specimen in thetest coili the dissimilarity will be 1 indicated by either or both of the galvanometers and the unsatisfactoryv material may be rejected ;by the operator. This method of operation. how-- ever, merely indicates some magnetic or electrical dissimilarity. While satisfactory in many instances, as for example when it is necessary to sort a mixed lot of bars which look alike but are metallurgicallybr chemically different, this "method of operation does not permit the determination of-a particular type of metallurgical variation. 'When a particular type of metallur-' gical'yariation is. sought, the following preliminary steps are taken:

Assuming that it. is vdesired to determine the .hardness of strip material, a good. strip a .all desired characteristicsis first placed in the,

test coil assembly, and with the phase shifter bridge set arbitrarily (as described hcreinbcfore) the potentiometers 82A and 13 are adjusted until the galvanometers read zero. Then the good strip is replaced by one of the samekindexcept 'that it is excessively hard. This will probably cause a deflection, at both galvanometers. The deflection of one of the gaivanoi'neters (say ll) is reduced to zeroby adjusting the phase shifter '5 bridge. Thehard strip is then replaced by'the good strip and the two galvanometers are again brought to 'zero position by adiusting the potentiometers 61A and il. The procedure is repeated until. the hard strip produces deflections at one 7 0;

galvanometer (say SI) and no deflection at the other (sayll); without requiring a shift of the potentiometers'flA and; 13 to attain zero readings ongjthe galvanometers when the hard bar is through the test coil assembly at high speed. At

Bars to be inspected'may now be passed are of too short duration to cause movement of the galvanometers. Metallurgical dissimilarities,

however, are usually manifested throughout the entire length of a bar or other specimen, so that the galvanometers have suillcient time to note a deflection due tothese causes.

I claim:- I p 1. In a magnetic analysis apparatus the combination which comprises an' exciter coil disposable ininductive relationship with a magnetizable body, means for energizing the exciter coil with an alternating current, a secondary coil disposed in inductive relationship with the exciter coil and connected to a circuit containing an adjustable phase shifter and means for introducing into the circuit a plurality of auxiliary alternating potentials of the same frequency as that supplied to the exciter coil but displaced from each other by substantially constant phase angles, and means for determining changes of phase and amplitude of an alternating potential in said circuit. a

2. Apparatus in accordance with claim 1 wherein the means through which the auxiliary potentials introduced into the; circuit are a plurality of center tap potentiometers provided with sliders and having their ends connected to sources of auxiliary potentials and their center taps and sliders connected to the circuit.

3. Apparatus in accordance with claim 1 wherein the means" for determining the changes in phase and amplitude-of the potential in. the circuit comprises a plurality of mixing transformers to the primary coils of which are supplied the potential undergoing investigation and the auxiliarypotentials, rectiflers connected with the secondary coils of the mixing transformers, and

- a plurality of direct current galvanometers connected respectively to the rectifiers.

4. In a magnetic analysis apparatus provided with an exciter coil and .a secondarycoil disposed in inductive relationship therewith and adapted to producean induced alternating potential influenced by a mag etizable bodly placedin inductive relationship therewith, the improve:

,ment which comprises a circuit connected to the in said circuit, means for introducing two auxiliary potentials 90 phase displaced from each i other into the circuit containing the phase-shifted potential, an even number of mixing transiformers provided withmultiple primary coils and with secondary coils, means for introducing the phase-shifted potential into a primary coil of each mixing transformer, means for introducing one auxiliary potential into primary coils in half of the mixing transformers, means for introducing the other auxiliary potentials into primary coils of the other half of the mixing transformers,

, rectiflers connected with the secondary coils of the mixing transformers, and direct current galvanometers connected to the rectifiers.

'5. In a magnetic analysis apparatus containing an exciter coil disposable in inductive relationship with a magnetizable body, means for energizing the exciter coil with alternating current,

and a secondary coil disposed in inductive rela-- tionship with the exciter coil, the improvement which comprises a'phase shifter connected to the secondary coil, an amplifier connected to said phase shifter, a matching transformer having its in the auxiliary potentials supplied to the circult are derived from the alternating current employed t9 energize the exciter coil.

'7. Apparatus in accordance with claim 5 wherein the circuit is provided with a pair of potentiometers having sliders and center taps through which the auxiliary potentials are supplied to the circuit. i

8. In a magnetic anaiysisapparatus the combination which comprises anexciter coil disposable in inductive relationship with a magnetizable body, means for energizing the exciter coil with an alternating current, a secondary coil disposed in inductive relationship with the'exciter coil and connected to a circuit containing means for introducing into the ,circuit a plurality.

of auxiliary alternating potentialsof the same frequency as that supplied tothe exciter coil but displaced from each other by substantially constant phase angles, and means for determinchanges of phase and amplitude of an alternating potential in said circuit. 1 r

' 'nmopon ZUSCHLAG. 

